1. Field of Invention
The invention relates to bar clamps and more particularly to such a bar clamp having an improved release mechanism which is adapted to smoothly release the clamping action of the bar clamp by two continuous steps.
2. Related Art
A main portion of a conventional bar clamp is shown in FIG. 1. The bar clamp comprises a driving key 10 including a forward first key plate 11, an intermediate second key plate 12, a plastic first pad 13 sandwiched between the first key plate 11 and the second key plate 12, and a rear first spring 16 urged against the intermediate second key plate 12, and a trigger handle 15 having an inner end pivotably secured within a housing of the bar clamp and engaged with a front surface of the forward first key plate 11.
The bar clamp further a locking key 20 spaced from a rear of the first spring 16. The locking key 20 comprises a forward third key plate 21, an intermediate fourth key plate 22, a plastic second pad 23 sandwiched between the third key plate 21 and the fourth key plate 22, and a rear second spring 24 urged against the intermediate fourth key plate 22, and a release handle 25 having an inner end pivotably secured within the housing of the bar clamp and engaged with a front surface of the forward third key plate 21. The release handle 25 is substantially parallel with the trigger handle 15 and is projected out of the front of a handle grip of the bar clamp. A slide bar 14 is disposed through the second spring 24, a slot 221 of the intermediate fourth key plate 22, a slot of the second pad 23, a slot 211 of the forward third key plate 21, a slot of the release handle 25, the first spring 16, a slot 121 of the intermediate second key plate 12, a slot of the first pad 13, a slot 111 of the forward first key plate 11, and a slot of the trigger handle 15 to terminate at a movable jaw carrier.
In a standby position, the driving key 10 is oriented perpendicularly relative to a longitudinal axis of the slide bar 14, and the locking key 20 is slightly inclined relative to the longitudinal axis of the slide bar 14. Thereafter, a user may repeatedly squeeze the trigger handle 15 toward the handle grip by holding with one hand to move a movable jaw toward a fixed jaw by incrementally advancing the slide bar 14. The clamping action can be stopped when a work piece is tightly secured by the jaws. To the contrary, activation of the release handle 25 in opposition to the second spring 24 tilts the locking key 20 into a position perpendicular to the longitudinal axis of the slide bar 14. Next, the slide bar 14 can travel freely to release the interference fit between the locking key 20 and the slide bar 14 so as to allow the movable jaw to move away from the fixed jaw. As an end, the work piece is released.
However, the conventional the bar clamp suffered from a couple of disadvantages. For example, the slots 111, 121, 211, and 221 are subject to wear after a period time of use. As a result, the desired locking force exerted by the locking key 20 is reduced greatly. It is typical that a user has to exert a substantial force in the clamping action after a period time of use. This is not desirable. A precise machining of the slots 111, 121, 211, and 221 can overcome the above drawback. But its cost is very high. In addition, the pads 13 and 23 can hinder the locking or driving action of the slide bar 14 after a period time of use as experienced by many users. Thus, the need for improvement still exists.